A cyclist with a stinky cracked helmet (Inset: one of the odoriferous microcapsules)

Article Summary

We’re told that we should replace our bike helmets every couple of years or so, because minuscule cracks can develop over time, rendering them structurally unsound. For the same reason, we’re supposed to replace a helmet that has withstood a direct impact immediately, no questions asked. The problem is... it’s so hard to get yourself to throw away what looks like a perfectly good helmet, just because it might no longer be effective. New technology developed at the Fraunhofer Institute for Mechanics of Materials should eliminate this situation. When your helmet is getting past its prime, it will start to smell. If it develops any large cracks... well, you’d better plug your nose.